Press F. The window shrinks to what a small device is
actually showing — and the receiver stops reading everything else.
This field is … megapixels. Sending all of it takes
… — more than your home connection. A native-detail
… window out of it takes …, which a phone
on 4G carries without noticing, because the other … is
never requested.
Nothing is cropped or re-encoded for you. Every viewer reads different
bytes of the same file, so a hundred people can each watch a different
part of this at once and the server does no work at all.